The present invention relates to a control system for a plant, and more particularly to a control system for controlling a plant with a sliding mode controller based on a sliding mode control theory which is one of robust control theories.
A sliding mode controller is known from Japanese Patent Laid-open No. 2000-110636, for example. The sliding mode controller controls a plant with a sliding mode control using a controlled object model which is obtained by modeling the plant.
The sliding mode control is a high gain control which generally has an advantage of a high control speed. On the other hand, the sliding mode control has a characteristic that an overshoot with respect to a control target value may often occur. Therefore, when controlling a throttle valve actuating device which actuates a throttle valve of an internal combustion engine, using the sliding mode control, it is very important to suppress the overshoot. Specifically, if the overshoot occurs in the control of the throttle valve actuating device, this causes a collision of the throttle valve with a full-closed position stopper, or an inconvenience that an output of the internal combustion engine increases to a value which is greater than the required value. Accordingly, it is particularly important in the control of the throttle valve actuating device to reliably prevent such inconveniences.
However, according to the control system employing a conventional sliding mode controller, suppression of the overshoot is not sufficient, and further improvement is desired.